1. Field of the Invention
This invention relates to novel perfluoropolyether derivatives. The invention also relates to lubricants and magnetic recording mediums using such derivatives.
2. Description of the Prior Art
Magnetic recording mediums of the type which comprise a non-magnetic support and a magnetic layer formed on the support by vacuum deposition of a ferromagnetic metal have a very good smoothness on the surface of the magnetic layer. This leads to a substantial increase in contact area with a magnetic head and sliding members such as guide rollers, with the attendant problem that the coefficient of friction is increased and the magnetic layer is liable to be sticked over or attached intimately to such members, resulting in poor runnability and durability.
In order to solve the problem, studies have been made on various types of lubricants. Attempts have been heretofore made to coat higher fatty acids or esters thereof on the top of the magnetic layer of the medium so as to decrease the coefficient of friction.
Very severe characteristics have been required for the lubricants which are employed in the magnetic recording medium. Unfortunately, existing lubricants have not cleared up all the requirements.
More particularly, the lubricant which is successfully used in the magnetic recording medium should meet the following requirements.
1) Good low temperature characteristics for ensuring an appreciable effect of lubrication on use in cold districts.
2) Capability of being applied very thinly in view of the spacing from a magnetic head, under which satisfactory lubricating characteristics are shown.
3) Standing repeated use over a long term with a lasting effect of lubrication.
Hitherto employed higher fatty acids and their esters tend to be frozen or solidified under low temperature conditions of not higher than 0.degree. C., thereby impeding the function as a lubricant and also to be short of long-term durability. Instead, there have been studied fluorine-based lubricants such as perfluoropolyethers. The perfluoropolyether is disadvantageous in that it is not dissolved in organic solvents other than freons.
In the field of the magnetic recording medium, practical characteristics such as runnability, durability and the like have been left as unsatisfactory owing to the shortage of the capability of lubricants used.